Index-only scan on GIN index for COUNT() queries

hi,

We have a GIN index on jsonb_col. We always get Bitmap Index Scan +
Bitmap Heap Scan when we do things like

SELECT COUNT(*) FROM mytable WHERE jsonb_col ? 'key1'

Theoretically, could support be added for Index-only scans on GIN
indexes when only a COUNT() is requested?

Thanks,
Seamus

PS. Here is the real query analyze:
https://gist.github.com/seamusabshere/b9d72132361fa598f7a431fa1bcb120f

--
Seamus Abshere, SCEA
http://faraday.io
https://github.com/seamusabshere
http://linkedin.com/in/seamusabshere